In a line photographing process for photo-engraving, an original is made by applying a photocomposing character, a hand written character, an illustration, or a halftone-dotted photograph. This original is photographed with a process camera. The process camera is designed so that the exposure is controlled to a specific exposing time, and a photographic material having a higher sensitivity can be subjected to photographing in a short time.
In recent years, there has been a need to shorten delivery dates in the printing industry, which requires a photographic material having a higher sensitivity. In order to meet this requirement, the sensitizing dyes described in JP-A-55-45015 (the term "JP-A" as used herein means an unexamined published Japanese patent application) have so far been used. Further, it is known from JP-B-48-35373 (the term "JP-B" as used herein means an examined Japanese patent publication) and U.S. Pat. No. 4,835,093 that a higher sensitivity may be obtained by incorporating a metal compound having a cyanide ligand such as potassium hexacyano ferrate (II) into a silver halide grain. However, these metal compounds have the problem that the use thereof in an excessive amount is likely to cause a lowering of contrast. Further, it is known that chemical sensitization with a selenium sensitizer increases sensitivity. However, this sensitization has the defect that the use thereof in an excessive amount is likely to generate a fog.